1. Field of the Invention
The present invention relates to a timer circuit used for a motor drive control apparatus or the like and a time count method.
2. Description of the Related Art
Hitherto, in an image forming apparatus such as an MFP (MULTI FUNCTION PERIPHERAL), a copying machine or a printer, a stepping motor is used in order to control the rotation of a photoconductive drum or a transfer belt. The stepping motor is a motor to supply a specified exciting pattern to a driver and to perform driving, can perform a rotation control by a step angle corresponding to the supplied exciting pattern, and is used in a wide field.
A control device of the stepping motor includes a timer, generates a clock signal based on a reference timing signal generated by the timer, and creates the exciting pattern by using this clock signal. Accordingly, the rotation speed can be controlled by arbitrarily setting the period of the timing signal from the timer.
There are needs for further improvement in performance and for speedup in the image forming apparatus. In order to address the needs, the speedup of the stepping motor control is indispensable, and therefore, the timer is required to achieve higher resolution and to have more bits.
In general, in order to increase the resolution of the timer, it is possible to take measures of raising the clock frequency as the reference. At this time, unless the number of bits of the timer is increased, the countable maximum time becomes small, and therefore, in the motor control in which acceleration and declaration are gradually made to a specified speed, the count number of the timer is insufficient.
In a technique disclosed in JP-A-10-63357, two timers each having a small number of bits are used to realize the control equivalent to the case were one timer having a large number of bits is used, and further, the PWM period is made long to realize the control in which the resolution can be made fine.